1. Technical Field
The present invention relates to a hearing aid processing apparatus which performs hearing aid and an adjustment apparatus.
2. Background Art
Hearing losses which require hearing aid are roughly divided into a conductive hearing loss and a sensorineural hearing loss depending on damaged parts.
In the case of a conductive hearing loss, an audio cannot be easily transmitted to an inner ear. However, once a vibration of the audio reaches the inner ear, a signal is transmitted through a route from auditory nerves without disturbances. Accordingly, impaired hearing ability is compensated by simply amplifying the audio inputted to the ear.
On the other hand, in the case of a sensorineural hearing loss, a vibration of an audio is transmitted to an inner ear as in the case of normal hearing people, but the nerves cannot be sufficiently excited due to deformation or loss of sensory cells. It is known that a sensorineural hearing loss decreases various auditory functions compared to the case of normal hearing people. Representative auditory characteristics include a loudness recruitment phenomenon, a decrease in frequency selective, a decrease in temporal resolution.
In the case of a sensorineural hearing loss, the minimum audible value is higher than that of normal hearing people, but a discomfort threshold value indicating a degree of discomfort caused by a loud audio does not vary from that of the normal hearing people. For this, once an audio reaches strength equal to or greater than the minimum audible value, loudness which is the sensory magnitude of the audio increases suddenly. This is called a loudness recruitment phenomenon.
Most of conventional hearing aids made focusing on such loudness recruitment phenomenon caused by a conductive hearing loss or a sensorineural hearing loss amplify the level of an input audio according to impaired degrees of hearing ability characteristics to reproduce audios. Other exemplary conventional hearing aids include a pair of monaural hearing aids which are separately mounted on right and left ears for binaural reproduction.
On the other hand, a decrease in frequency selective increases the influence of masking between frequency band components, in particular, the influence of masking of high frequency components by low frequency components (upward masking).
Hearing aid processing aiming to increase clarity of an input audio signal by reducing masking between frequency bands includes dichotic listening in which the input signal is divided on the frequency axis to be presented at the respective ears.
For example, in a report (see Non-patent Reference 1, for example), in the case where an audio is divided into two bands of a low band and a high band, and the low band and the high band are separately presented to the respective right and left ears of a hearing impaired person, the clarity of the audio is higher than the clarity obtained in the case where both the high and low bands are presented to one of the ears of the hearing impaired person.
In addition, in a report (see Non-patent Reference 2, for example), an audio clarity obtained from a person who suffers from a sensorineural hearing loss is increased in a shown hearing aid processing of dividing an audio band into eighteen frequency bands and alternately assigning the adjoining bands to the respective right and left ears.
Non-patent Reference 1: Barbara Franklin, “The Effect of Combining low- and high-frequency passbands on consonant recognition in the hearing impaired”, (US), Journal of Speech and Hearing Research, 1975
Non-patent Reference 2: D. S. Chaudhari and P. C. Pandey, “Dichotic Presentation of Speech Signal Using Critical Filter Bank for Bilateral Sensorineural Hearing Impairment”, (US), Proc. 16th ICA, 1998
Non-patent Reference 3: B. J. C. Moore et. al., Chokaku shinrigaku gairon (General auditory psychology), pp. 105-108, Seishin Shobo, 1994